The present invention relates generally to the field of telecommunications and, in particular, to systems and methods for reverse path upstream signaling.
Cable networks are a common medium for providing video, audio and other data or programming to subscribers. Conventionally, cable networks have one or more head ends that transmit signals to subscribers over a medium that includes coaxial cable. Cable networks typically provide subscribers with programming on a variety of channels. Each channel occupies a distinct frequency band on the coaxial cable.
Signals transmitted over a coaxial cable tend to attenuate or decrease in signal strength or magnitude as the signals propagate away from the head end. Cable networks typically include network amplifiers that are placed at various locations in the cable network. The network amplifiers increase the magnitude of the signals to compensate for the attenuation due to the distance that the signals have propagated.
The attenuation in the magnitude of signals transmitted over coaxial cable further varies with the frequency of the signals. This is due to the xe2x80x9cfrequency responsexe2x80x9d of the coaxial cable. Significantly, the frequency response of a particular coaxial cable depends on the parameters in the construction of the coaxial cable such as, the characteristic impedance of the cable, the inner diameter of the outer conductor, the outer diameter of the inner conductor, the strand factor (K1), the braid factor (K2), the power factor, and the dielectric constant of the insulator of the cable among other parameters. Generally, however, the frequency response of a coaxial cable has a downward or negative slope with increasing attenuation as frequency increases. This is often referred to as xe2x80x9ccable tiltxe2x80x9d or xe2x80x9ccharacteristic attenuation,xe2x80x9d e.g., the cable loss at a maximum frequency for the cable network subtracted from the cable loss at the minimum frequency for the cable network.
To compensate for cable tilt, as well as to detect other operating difficulties, network amplifiers often include status monitors. These status monitors are designed to provide signal alarms or other monitored condition reports back to the head end of the cable network. It is undesirable for status monitoring signals sent upstream to affect the mainline signal which is being transmitted downstream to the end user, or subscriber. The less intrusive status monitoring can be the better, especially from a cost standpoint and RF gain.
Conventionally, detecting operating difficulties involves using directional couplers at the network amplifier in the cable network. On downstream signaling, a directional coupler picks-off signals from the main signal path when data is requested by the head end. A response to the request is injected into the upstream signal via a second directional coupler. However, the presence of each directional coupler introduces an insertion loss, conventionally expressed in decibel (dB), into the downstream and upstream signal paths, respectively. An insertion loss, caused by a directional coupler, conventionally requires additional amplification in the corresponding signal path. Requiring additional amplification in the upstream signal path introduces additional noise. As a result RF gain is impacted which results in added cost to mitigate any loss in network performance.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for systems and methods for improved reverse path upstream signaling.
The above mentioned problems with reverse path upstream signaling and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A reverse path signaling circuit is described which provides less noise and interruption when injecting signals upstream to a head end.
In one embodiment, a reverse path signaling circuit is provided which includes a low pass filter, a status monitor, and a common emitter amplifier. The common emitter amplifier has a single-ended emitter injection region which couples to the status monitor. The status monitor injects status monitor signals into the single-ended emitter injection region for passing the status monitor signals upstream to a head end. The low pass filter is coupled to another input on the common emitter amplifier. An output from the common emitter amplifier is taken at a collector region. The reverse path signaling circuit of the present invention does not require the use of a directional coupler as part of the circuit.